Engineering Definitions of Terms
"A" "B" "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
"N", "O", "P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z"

Onboard Diagnostics Terms

Basic I/M: A vehicle inspection and maintenance program designed to meet the basic I/M performance standard which includes performance of an idle test on 1968+ passenger cars. Under the 1990 Amendments to the Clean Air Act, basic I/M is required in moderate non-attainment areas, as well as those areas already implementing or required to implement a basic I/M program prior to passage of the 1990 Amendments.

"Check Engine" Light: See the definition for Malfunction Indicator Light (MIL) below.

Diagnostic Trouble Codes: [DTC] An alphanumeric code which is set in a vehicle's onboard computer when a monitor detects a condition likely to lead to (or has already produced) a component or system failure, or otherwise contribute to exceeding emissions standards by 1.5 times the certification standard.

Enhanced I/M: A vehicle inspection and maintenance program designed to meet one of three enhanced I/M performance standards; high, low, and ozone transport region (OTR) low. The high enhanced standard is designed around IM240 tail-pipe testing and purge and pressure evaporative system testing. The low enhanced standard is similar to the basic I/M performance standard, but includes light-duty trucks and a visual anti-tampering inspection. The OTR low enhanced performance standard is designed for areas which would not be required to do I/M at all, save for their location within the Northeast Ozone Transport Region. The OTR low enhanced standard is based upon tail-pipe testing using remote sensing devices and visual anti-tampering inspections. Serious and worse non-attainment areas are required to implement enhanced I/M, as well as all areas within the OTR with populations over 100,000, regardless of attainment status.

Environmental Protection Agency: [EPA] The government agency that sets the requirements for OBD in the US. Some OBD history.

European On-Board Diagnostics: [EOBD], sometimes as Europe On-Board Diagnostics.

Evaporative System Test: A test of a vehicle's evaporative control system to determine if the system is 1) leaking and/or 2) purging properly.

Gross Vehicle Weight Rating: [GVWR]

Malfunction Indicator Light: [MIL] Also known as a Check Engine light, the Malfunction Indicator Light of MIL is illuminated on the dashboard when conditions exist likely to result in emissions exceeding standards by 1.5 times or worse. Alternatives include "Service Engine Soon," as well as an unlabeled picture of an engine.

Onboard Diagnostics: [OBD] A system of vehicle component and condition monitors controlled by a central, onboard computer running software designed to signal the motorist when conditions exist which could lead to a vehicle's exceeding its emission standards by 1.5 times the standard.

OBD Data Link Connector (DLC): OBD [DLC] The interface is usually located under the dashboard on the driver's side or between a vehicle's OBD computer and the OBD scanner. Connecting an OBD scanner to the DLC allows I/M inspectors and vehicle repair technicians to read the readiness status of the vehicle's various onboard monitors as well as any diagnostic trouble codes (DTCs).

Readiness Code: A status flag stored by a vehicle's onboard computer which is different from a DTC in that it does not indicate a vehicle fault, but rather whether or not a given monitor has been run (i.e., whether or not the component or system in question has been checked to determine if it is functioning properly).

Scanner or Scan Tool: A PC-based or handheld device used to interface with a vehicle's onboard computer for the purpose of reading DTCs and monitor readiness status.

Test-and-Repair: An I/M program which allows the same people who test a vehicle to also repair the same vehicle and retest it to determine whether or not the repairs performed were adequate. Test-and-repair programs are also generally decentralized, though not all decentralized programs are necessarily test-and-repair.

Test-Only: An I/M program, usually, though not exclusively centralized, which requires that the functions of testing and repair be performed by different, financially unrelated parties.

Vehicle Communications Module: [VCM].

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